This invention relates to electrostatographic copying and more specifically to an improved photosensitive material for use in binder type xerographic photoreceptors.
The art of xerography involves the use of a photoconductive element or plate which is uniformly electrostatically charged in order to sensitize its surface. The plate is then exposed in an imagewise manner to activating electromagnetic radiation which selectively dissipates the charge in the exposed areas of the photoconductive material while leaving behind a latent electrostatic image in the non-exposed areas. This latent electrostatic image may then be developed by depositing a finely divided electroscopic marking material on the surface of the photoconductive material. This concept was originally disclosed by Carlson in U.S. Pat. No. 2,297,691 and is further amplified and described in many related patents.
One type of photoconductive layer used in xerography is disclosed in U.S. Pat. No. 3,121,006 to Middleton and Reynolds which describes a number of binder layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an organic electrically insulating resin binder. In the particular examples of the binder systems described in Middleton et al., the dispersion of photoconductive particles is relatively uniform, such uniformity having been accomplished by thorough mixing of the resin and photoconductive particles. With these uniform dispersions a relatively high volume concentration of photoconductor particles, 40 to 60 and preferably about 50 percent by volume, is normally used to obtain the requisite particle-to-particle contact necessary for rapid discharge.
There is an ongoing need for improved photoconductive materials for use in the above-described binder layer photoreceptors. In the synthesis of group II chalcogenides for employment in binder layer photoreceptors, it is possible to employ well known doping techniques to achieve photosensitivity much greater than that of zinc oxide. These preparation methods require the incorporation into the lattice of small quantities of elements such as copper, chlorine, gallium, aluminum, etc., which is normally accomplished by multiple firing of the materials in the presence of a fluxing or mineralizing agent. Resistive, highly sensitive photoconductors have been prepared in this way, however, this method inherently leads to a relatively large particle size, 1-30 .mu., which places severe limitations on the use of these materials in fabricating electrostatographic photoreceptors. This is especially true in terms of the resultant high background density and limited mechanical properties encountered with layers having a high volume loading of photoconductor.
It is well known that group II chalcogenides, e.g. CdSSe, manufactured as pigments are photosensitive and can be utilized in the fabrication of electrostatographic layers. These materials possess the advantage of a particle size which ranges from 0.001 to 1 .mu. and are, therefore, eminently more suited to the formulation of xerographic photoreceptors than presently available doped materials. Two major problems have restricted the use of these materials in the past. They are: (1) a comparatively low order of sensitivity as compared to the doped materials and (2) the inability to consistently produce a material having the same electrical characteristics by presently known processes.
Accordingly, it would be desirable, and it is an object of the present invention to provide a novel process for the production of cadmium sulfoselenide pigments which are highly photosensitive and therefore useful as photoconductive materials in electrostatographic copying.
A further object is to provide such a process which produces cadmium sulfoselenide which consistently exhibits characteristics which render it useful for electrostatographic copying.
An additional object is to provide a cadmium sulfoselenide pigment which may be used in the preparation of a binder layer xerographic photoreceptor.